The invention relates to a coextrusion nozzle arrangement with a distributor portion associated with an extruder for delivery of an extrudate to a nozzle portion for coextrusion of the extrudate.
Such nozzle arrangements are common in extruders or extrusion devices. A known coextrusion nozzle head is commonly mounted on at least one extruder in such a way that the nozzle set can be exchanged with another nozzle set, to manufacture, for example, other pipe diameters, layered pipe profiles, or the like. The connection region between the nozzle portion and the distributor portion of the nozzle head, which is exchanged only rarely, must thereby be able to withstand significant pressures.
When a nozzle set of a coextrusion nozzle head is exchanged, the various portions of the nozzle set with which the nozzle head is equipped, must, according to the prior art, be removed one after the other from the distributor portion of the coextrusion nozzle head and cleaned from extrudate. Thereafter, the corresponding portions of the nozzle set with which the production device is to be refitted, must be installed. The various portions must thereafter be aligned and adjusted for the extrusion of a usable product. This alignment requires significant time. Furthermore, a flawed product is produced during the alignment process, which cannot be economically used. Thus, very expensive machinery, an extruder and production machinery connected thereto, such as a corrugator, are deactivated over an extended a period of time, until the refitting of the ejection head is completed.
During the disassembling and cleaning of the portions of the nozzle set in the hot condition, there is a risk of accident and damage. This means that the dismantling of the nozzle parts brings with it a not insignificant risk of damage and the cleaning of the nozzle parts must be carried out in the hot condition, whereby reheating with a heat source is necessary. This is a costly process which leads to scratching of the surface of the nozzle parts, whereby scratches must later be removed by polishing. This respectively leads to a material removal, which in the end causes wear.
During the installation of the new coextrusion nozzle set and the subsequent alignment steps, very significant, preferably also acentrical forces act on the exchanged coextrusion nozzle set, which forces subject the nozzle set to high mechanical loads and can very significantly reduce its service life.
Thus, according to the prior art, one must in some way or another put up with long downtimes, material waste, as well as wear on the nozzle set of the nozzle head itself for the readjustment of an ejection head from one product to another.
It is an object of the present invention to further develop generic nozzle arrangements so that the mentioned disadvantages are overcome at least in part.
In particular, it is an object of the invention to enable a quick exchange of a coextrusion nozzle set.
This object is achieved with a nozzle arrangement wherein a mounting and connecting base is provided between the distributor portion and the nozzle portion.
Preferably, it is thereby possible to maintain the exit nozzle portion in a predetermined installation arrangement, which is also maintained relative to the distributor portion during the removal of the mounting and connecting portion together with the nozzle portion. If later another nozzle portion, which is also preadjusted and fixed on a mounting and connecting base, is mounted onto the distributor portion of the nozzle arrangement of the ejection head, practically no alignment or test run of the ejection head is necessary for the manufacture of a finished product.
It is further possible, since little alignment of the nozzle portion of the coextrusion nozzle set is necessary, to install the whole nozzles preheated to a desired operating temperature which is selected for a specific plastic, so that the refitting, installation and preheating times which otherwise take away from the production time, can be further reduced.
If alignment steps are necessary, they are very significantly reduced relative to the prior art, if not even negligible.
The mechanical loads on the nozzle set can be significantly reduced, since additional stress by alignment is significantly, if not completely avoided.
Of course, the mounting and connecting base can also be made of several portions and thus need not necessarily be made in one piece. The one-piece construction is preferred for the installation connecting base. However, a two part mounting and connecting base, for example, can also provide, to a reduced extent, the above mentioned features according to the invention. For example, it is possible to separately mount centrally inwardly positioned portions of a coextrusion nozzle set and to mount onto the distributor portion only further outwardly located portions of the nozzle which are preinstalled on the mounting and connecting base.
The mounting and connecting base preferably also includes a respective guide channel which conducts the extrudate from the distributor portion to the nozzle portion. The distributor portion and/or the nozzle portion can thereby include channel extensions which bridge the distance between these portions, whereby the mounting and connecting base used includes corresponding recesses for the receiving of the channel extensions. In this case it is possible to reduce the number of seals so that, although the mounting and connecting base is located between the distributor portion and the nozzle portion, the number of seals is reduced to the number of seals necessary according to the prior art, since only one abutment plane exists for the supply conduits, whereby the openings for the connecting webs must also be sealed.
In order to guarantee a sufficient sealing of the nozzle arrangement in accordance with the invention, even at the high pressures to which the extrudate must regularly be exposed, it is advantageous when sealing means are provided at the respective abutment locations or planes. For example, seals can be provided between the aforesaid channel extensions and the surrounding distributor and/or nozzle portion. If the sealing surfaces are displaced onto the mounting and connecting base, corresponding sealing means are provided accordingly on their sides directed towards the respectively connecting portions or on the connecting portions themselves.
It has proven especially advantageous when sealing means are used which upon a pressure load automatically provide a larger sealing effect. The sealing action of a corresponding sealing means can increase over a large pressure range proportionally with or dependent on the pressure, which means it is not necessary to apply mechanical forces which adjust a seal to the maximum expected pressure load, since the sealing means itself automatically adjusts its sealing action to the pressure load. Liquid material, which exits in the case of a leak exerts a pressure on the geometrical shape of the seal which leads to a stronger pressing of the sealing surfaces of the seal onto the surrounding device portions so that leaks can be sealed. Ductile metals can also be used for the seals. For example, copper, tin or the like can be used herefor.
The mounting and connecting base is preferably made of several, for example, concentrically positioned, annular disks between which annular connecting conduit gaps are provided for the passage of the extrusion mass.
On the other hand, the installation or connecting base can advantageously also be constructed in the shape of a webbed disk and/or an apertured disk so that the extrudate to the transported can be guided through the apertures or in between the webs.
At least one centering arrangement is preferably provided for the centering of the mounting and connecting base relative to the distributor portion and to align or center the portions of the nozzle set relative to the mounting and connecting base. Respective centering and alignment arrangement are preferably provided, so that a centering can be carried out, for example, by adjustment of one or more bolts or screws.
The nozzle arrangement in accordance with the invention can of course also be constructed for more than two extrudate streams. The present invention is especially advantageously useable for extrusion products with more than two layers, for which the alignment would be even more complicated and costly.